How to convert a variable of data type uint8_t to int32_t using Neon? I could not find any intrinsic for doing this.
Assuming you want to convert a vector of 16 x 8 bit ints to four vectors of 4 x 32 bit ints, you can do this by first unpacking to 16 bits and then again to 32 bits:
// load 8 bit vector
uint8x16_t v = vld1q_u8(p); // load vector of 16 x 8 bits ints from p
// unpack to 16 bits
int16x8_t vl = vreinterpretq_s16_u16(vmovl_u8(vget_low_u8(v))); // 0..7
int16x8_t vh = vreinterpretq_s16_u16(vmovl_u8(vget_high_u8(v))); // 8..15
// unpack to 32 bits
int32x4_t vll = vmovl_s16(vget_low_s16(vl)); // 0..3
int32x4_t vlh = vmovl_s16(vget_high_s16(vl)); // 4..7
int32x4_t vhl = vmovl_s16(vget_low_s16(vh)); // 8..11
int32x4_t vhh = vmovl_s16(vget_high_s16(vh)); // 12..15
来源：https://stackoverflow.com/questions/30528352/how-to-convert-unsigned-char-to-signed-integer-using-neon-simd